The present invention relates to an objective lens drive apparatus applicable to optical disk apparatus, and more particularly, to an objective lens drive apparatus that can drive an objective lens to focus onto an optical disk an optical beam from a light source, in a radial direction of the optical disk.
For example, in optical disk apparatus, information recorded on an optical disk is detected optically by an optical pickup provided so as to be movable in a radial direction. In order to focus light onto a predetermined track, this type of optical pickup is provided with an objective lens drive apparatus to drive an objective lens in a radial direction (the tracking direction). The inventor of the present application has proposed the following objective lens drive apparatus in U.S. patent application Ser. No. 472,745 (Filling Data Jan. 31, 1990). This apparatus has a base member that moves in a radial direction of a disk, a support unit that is provided on the base member, an objective lens supported by the support unit and a tracking coil provided to the support. When a drive current flows through the tracking coil, the field of the tracking coil with respect to the field of a magnet on the base member repulse each other and the light that passes through the position of the objective lens is controlled so that the light that passes thought the objective lens is focussed on the required track.
The support unit has an objective lens holder that directly supports the objective lens, and a supporting member that elastically supports the objective lens holder. The objective lens is supported by this supporting member so as to be movable in the direction of the radius of the optical disk. When the drive force from the tracking coil acts, the supporting member bends in the direction of the radius of the optical disk and so the objective lens is displaced in the direction of the radius of the optical disk. After the optical pickup itself has been moved by seek control, to the position of the objective track on the optical disk, this objective lens drive apparatus supplies a drive current to the tracking coil so the position of the objective lens is controlled (by tracking control) so that the optical beam passing through the objective lens is accurately irradiated to the objective track.
When there is seek operation to move the optical pickup in the direction of the radius of the optical disk, the light reflected from the recording surface of the optical disk is detected via the objective lens. Then, a track crossing signal is generated in accordance with the passing of the optical beam over the track on the disk. This track signal is used as the basis for determining the speed of movement of the optical pickup. A characteristics of this speed of movement is such that the speed of the optical pickup is controlled during seek operation so that it has the required characteristic.
It can be considered that in order to reduce the access time in optical disk apparatus, this seek operation should be made faster. If this is done, then it is necessary to move the optical pickup at a speed faster than that obtainable by conventional apparatus. If the seek operation is made faster, then the acceleration on the objective lens supported on the supporting member and the objective lens holder both become greater. This is, that the supporting member bends in the direction of the radius of the optical disk and the position of the objective lens deviates with respect to the base member, or the objective lens vibrates in the direction of the radius of the optical disk. As a result, the speed of detection of the optical pickup is no longer accurate with respect to the track cross signals that perform the seek operation.